General Science eBook

The principle just stated embodies one of the fundamental
laws of science, called the law of the conservation
of matter.

A similar law holds for energy as well. We can
transform electric energy into the motion of trolley
cars, or we can make use of the energy of streams
to turn the wheels of our mills, but in all these
cases we are transforming, not creating, energy.

When a ball is fired from a rifle, most of the energy
of the gunpowder is utilized in motion, but some is
dissipated in producing a flash and a report, and
in heat. The energy of the gunpowder has been
scattered, but the sum of the various forms of energy
is equal to the energy originally stored away in the
powder. The better the gun is, the less will
be the energy dissipated in smoke and heat and noise.

CHAPTER V

FOOD

55. The Body as a Machine. Wholesome food
and fresh air are necessary for a healthy body.
Many housewives, through ignorance, supply to their
hard-working husbands and their growing sons and daughters
food which satisfies the appetite, but which does not
give to the body the elements needed for daily work
and growth. Some foods, such as lettuce, cucumbers,
and watermelons, make proper and satisfactory changes
in diet, but are not strength giving. Other foods,
like peas and beans, not only satisfy the appetite,
but supply to the body abundant nourishment.
Many immigrants live cheaply and well with beans and
bread as their main diet.

It is of vital importance that the relative value
of different foods as heat producers be known definitely;
and just as the yard measures length and the pound
measures weight the calorie is used to measure the
amount of heat which a food is capable of furnishing
to the body. Our bodies are human machines, and,
like all other machines, require fuel for their maintenance.
The fuel supplied to an engine is not all available
for pulling the cars; a large portion of the fuel is
lost in smoke, and another portion is wasted as ashes.
So it is with the fuel that runs the body. The
food we eat is not all available for nourishment,
much of it being as useless to us as are smoke and
ashes to an engine. The best foods are those
which do the most for us with the least possible waste.

56. Fuel Value. By fuel value is meant the
capacity foods have for yielding heat to the body.
The fuel value of the foods we eat daily is so important
a factor in life that physicians, dietitians, nurses,
and those having the care of institutional cooking
acquaint themselves with the relative fuel values
of practically all of the important food substances.
The life or death of a patient may be determined by
the patient’s diet, and the working and earning
capacity of a father depends largely upon his prosaic
three meals. An ounce of fat, whether it is the
fat of meat or the fat of olive oil or the fat of any
other food, produces in the body two and a quarter
times as much heat as an ounce of starch. Of
the vegetables, beans provide the greatest nourishment
at the least cost, and to a large extent may be substituted
for meat. It is not uncommon to find an outdoor
laborer consuming one pound of beans per day, and
taking meat only on “high days and holidays.”